Conventional data transmission method on the Internet is peer-to-peer transmission or unicast transmission, in which data are transmitted from one sending end to one receiving end. However, in case where multicast data transmission is performed in the unicasting method to transmit the same data to many receiving ends, there are problems that the server of the sending has a great deal of load, and the bandwidth of the network is occupied inefficiently.
Furthermore, the problems with performing multicast transmission in the unicasting method become more serious, because the next-generation Internet is based on multimedia data transmission, and the volume of multimedia data is very big.
If the problem with the unicasting method is solved, it is possible to broadcast multimedia data stream, such as video and audio data. In short, although a stream of multimedia data is outputted from a sending end, i.e., media server, once through the Internet, the data stream can be transmitted to all the clients (of a multicast group), which are final receiving ends that desire to receive the data stream, selectively, which is multicast technology. When data is transmitted from the sending end, each client of the multicast group that desires to receive the data can receive the same duplication of the data.
Multicast technology is a mixture of the advantages of unicasting and broadcasting technologies. It enhances the network efficiency and reduces the confusion of a network. Since it duplicates data and transmits the duplicated data to the receiving ends that desire to receive the data, i.e., ones that belong to the multicast group, it prevents unnecessary data reception. Accordingly, an Internet service provider can convert its network into a multicast network using multicast equipment adopting the multicasting technology.
On a multicast network, broadcast data can be transmitted as many as the bandwidth allows on the network, no matter how many clients are connected thereto. For instance, if the allowed bandwidth of a cable TV network is 30 Mbps, 30 one-Mbps broadcast data or 60 500-Kbps broadcast data can be transmitted.
Despite the advantages of multicasting technology, there are many restrictions in converting the existing Internet into a multicast network. For instance, networking equipment that constitutes the Internet does not support the multicasting function, and it costs a lot of money to substitute the equipment with multicast-supporting equipment.
FIG. 1 is a diagram showing a conventional multicast network using a static tunneling technique. So far, to support the multicasting function, all the routers between the media server 101, i.e., sending end, and the clients 103, i.e., the final receiving ends should support the multicasting technology. So, if there are networks 105 and 107 that do not support the multicasting function in between, tunneling method should be used.
According to the conventional tunneling method, when ac router 105 between the sending end and the receiving end does not support the multicast function, a virtual path is formed between multicast-supporting routers 109 to exchange multicast data, and the router 105 that does not support the multicasting function simply relay the multicast data. Between the multicast-supporting routers 109 connected through the tunneling method, the multicast data is encapsulated in the form of a unicast IP packet and transmitted to the encapsulated multicast data by adding a header containing a tunnel source address and a tunnel destination address. So, it has no problem to pass the router 105 that does not support the multicasting function.
The conventional tunneling method is a static technique, so the multicasting function should be set up in the router 109 manually. Accordingly, the router 109 on the part of the media server 101, the sending end, and the router 109 on the part of the client 103 that requires multicasting should be set up with the multicasting function, which acts as a big burden for the Internet service provider, because it should respond to every request for multicast setup from a plurality of clients 103 that desire to receive multicast data.
Furthermore, recent increasing demand for establishing a home network leads to increasing request for multicast service. However, since most clients 103 use flexible IP addresses, it is impossible to establish a multicast network using a static tunneling method. In short, a fixed IP address is needed in order to set up the multicasting function in a router and perform static tunneling, but if a client has a flexible IP address, the multicasting function cannot be set up in the router.
FIG. 2 is a diagram illustrating a conventional multicast network using a peer-to peer (P2P) transmission technique. Since it becomes hard to modify the scheme of a router, a multicast method is developed recently that makes other clients receive data by making a client, which has received the data from the sending end in the unicasting method, upload the received data on the Internet and relay the data to other clients.
According to the multicasting method, a client 213 receives data from the data transmission server 207 of a network 201 having a data source 205 in the unicasting method, and the client 213 uploads the received data on the network 203, to which it belongs, and then other clients 215 and 217 on the network receive the data from the client 213.
In short, when a client of a network receives data, the client performs as a repeater and thereby other client on the same network can receive the data.
As networks are mainly formed of routers and many routers and switches support the multicasting function recently, using the routers to the maximum extent makes it easy to administrate the network and reduces errors. However, this multicasting method also have a problem that the performance is deteriorated due to the limit in the upload speed on an asymmetric network, such as xDSL or cable network.